Functional fluid containing azo benzene derivatives as antioxidants



United States Patent 3,413,225 FUNCTIONAL FLUID CONTAINING AZO BEN ZENEDERKVATIVES A ANTEUXHDANTS Basil Dmuchovsky and Richard W. Weiss, St.Louis, Mo.,

assignors to Monsanto Company, St. Louis, M0., a corporation of DelawareNo Drawing. Filed June 27, 1966, Ser. No. 560,790

16 Claims. (Cl. 252-475) ABSTRACT OF THE DISCLOSURE Compositions of theclass which exhibit improved oxidative resistance by the incorporationof an azo benzene compound into a class of base stocks representative ofwhich are polyphenyl ethers, polyphenyl thioethers, mixed polyphenylethers-thioethers, phenylmercaptobiphenyls, phenoxybiphenyls and mixedphenoxyphenylmercaptobiphenyls. The compositions have many uses, amongwhich are use as jet engine lubricants, heat transfer fluids andhydraulic fluids.

This invention relates to new phenoxy and thiophenoxy azobenzenecompounds, to functional fluid compositions having improved oxidativestability and more particularly to compositions comprising a functionalfluid and a stabilizing amount of an azo compound.

Many different types of materials have been utilized as functionalfluids and functional fluid: are used in many different types ofapplications. Such fluids have been used as electronic coolants, atomicreactor coolants, diffusion pump fluids, synthetic lubricants, dampingfluids, bases for greases, force transmission fluids (hydraulic fluids),heat transfer fluids, die casting release agents in metal extrusionprocesses and as filter mediums for air conditioning systems. Because ofthe wide variety of applications and the varied conditions under whichfunctional fluids are utilized, the properties desired in a goodfunctional fluid necessarily vary with the particular application inwhich it is to be utilized with each individual application requiring afunctional fluid having a specific class of properties.

Of the foregoing the use of functional fluids as lubricants,particularly jet engine lubricants, has posed what is probably the mostdifficult area of application. As the operating temperatures forlubricants have increased it has become exceedingly diflicult to findlubricants which properly function at these high temperatures for anysatisfactory length of time. Thus, the requirements of a jet enginelubricant are as follows: The fluid should possess high and lowtemperature stability, foam resistance, good storage stability and benoncorrosive to metal mechanical members which are in contact with thefluid. Such fluids should, in addition, possess adequatetemperature-viscosity properties and satisfactory lubricity, that is,the lubricants must not become too thin at the very high temperatures towhich they are subjected nor must they become too thck at lowertemperatures and must at the same time be able to provide lubricity oversuch range of temperatures. In addition, such lubricants should not formdeposits which interfere with the proper operation of a jet engine.

As the speed and altitude of operation of jet enginecontaining vehiclesincreases, lubrication problems also increase because of increasedoperating temperatures and higher bearing pressures resulting from theincreased thrust needed to obtain high speeds and altitudes. As theservice conditions encountered become increasingly severe theuseful-life of the functional fluid is shortened, primarily due to theirdeficiency in oxidative stability above 500 F. In general, as theoperating requirements of a jet engine are increased, enginetemperatures increase and oil temperatures in the range of 600 F. andhigher are encountered.

The useful life of any lubricant can be adjudged on the basis of manycriteria such as the extent of viscosity increase, the extent ofcorrosion to metal surfaces in contact with the lubricant and the extentof deposits. Those skilled in the art have found many ways to improvelubricants and to thus retard or prevent the effects which shorten theuseful life of a lubricant. Thus, it is a general practice to add smallamounts of other materials, or additives, to lubricants in order toaffect one or more of the properties of the base lubricant. It isdiflicult, however, especially as operating temperatures are increased,to find additives which will still perform the function for which theyare added and yet not inject other problems such as increasing corrosionand engine deposits.

As is seen from the foregoing temperature characteristics of a jetengine, a functional fluid can attain temperatures of up to 600 F. andhigher which can result in oxidative and thermal degradation of alubricant. The stabilization of lubricants at these high operatingtemperatures through the use of additives presents an extremely complexand difficult problem since antioxidants which have been utilized inlubricating oil compositions, such as phenolics and amine derivatives,decompose at such high temperatures thereby producing deposits andsludge. In addition, such decomposition products can at hightemperatures promote oxidation thereby subjecting a lubricant to anincreased rate of oxidative degradation. It is, therefore, a fundamentalrequirement for an antioxidant which is to be used in a high temperaturelubricant that it perform its desired function without forming sludge ordeposits. It is thus of particular importance that a functional fluidhave improved oxidation resistance without forming sludge and depositsin the many functional fluid systems and applications as aforedescribed.

It has now been found that the oxidative stability and thus the usefullife of functional fluids can be greatly extended, even under the severeconditions encountered in jet engines and other devices operating attemperatures of the order of 600 F. and higher, by the addition tofunctional fluids of an azo compound, said azo compound being selectedfrom (A) A compound represented by the structure wherein a and b arewhole numbers having a value of 0 to 5, R and R are each selected fro-mthe group consisting of alkyl, substituted alkyl, aryl, substitutedaryl, amino, substituted amino, cyano, nitro, halogen, sulfonic,carboxyl, carboalkoxy, phenoxy, substituted phenoxy, phenylmercapto,substituted phenylmercapto, alkoxy and hydroxyl and when a or b has avalue of 2 to 5 any two Rs or R s which are attached to adjacent carbonatoms within the phenylene ring can together form a carbocyclic orsubstituted carbocyclic ring, and

(B) Mixtures thereof.

The functional fluids, to which an azo compound is added to provide thecom-positions of this invention, hereinafter referred to as base stocks,include, but are not limited to, polyphenyl ethers, polyphenylthioethers, mixed polyphenyl etherthioethers, phenoxybiphenyls,phenylmercapto biphenyls, mixed phenoxy phenylmercapto biphenyls andmixtures thereof. 'It is also contemplated within the scope of thisinvention that the phenyl and phenylene groups in the aforedescribedbase stocks can be partially or totally replaced with a heterocyclicgroup such as thiophene and pyridene.

Whereas the incorporation of any foreign element into a base stock canalter properties of a functional fluid, the concentration of an azocompound in the base stock is adjusted in terms of the particular systemand the base stock which is utilized in this system to providefunctional fluid compositions of this invention which contain additiveamounts of an azo compound sufficient to improve the oxidative stabilityof a base stock while not adversely affecting critical base stockproperties. It has generally been found that the preferred additiveconcentrations of an azo compound for the base stocks described aboveare generally from about 0001 Weight percent to about 10 weight percent,preferably from about 0.05 weight percent to about 5 weight percent.

Therefore, included within the present invention are compositioncomprising a base stock and a Stabilizing amount of an azo compound,that is, an azo compound is added, in a concentration sutficient toimprove the oxidative stability of the base stock. The functional fluidcompositions of this invention can be compounded in any manner known tothose skilled in the art for the incorporation of an additive into abase stock as for example by adding an azo compound to the base stockwith stirring until a homogeneous fluid composition is obtained.

Typical examples of azo compounds are Typical examples of base stockswhich are suitable as base stocks for this invention are represented bythe structure 4)a wherein A, A A and A are each a chalkogen having anatomic number of 8 to 16, X, X X X and X each are selected from thegroup consisting of hydrogen, alkyl, haloalkyl, halogen, phenyl,alkaryl, hydroxyl, alkoxy, aralkyl and substituted aralkyl; w, y and zare whole numbers each having a value of 0 to 8; c is a whole numberhaving a value of from 1 to 4; d is a whole number having a value offrom 1 to 5 and e is a whole number having a value of 0 to 1 providedthat when e is 0, y can have a value of 1 to 2. Typical examples of suchbase stocks are 2- to 7-ring 0-, mand p-polyphenyl ethers and mixturesthereof, polyphenyl thioethers and mixtures thereof, mixed polyphenyletherthioether compounds in which at least one of the chalkogensrepresented by A, A A and A is dissimilar with respect to any one of theother chalkogens, phenoxybiphenyls, phenylmercaptobiphenyls, mixedphenoxy phenylmercaptobiphenyls and mixtures thereof. It is alsocontemplated within the scope of this invention that the phenyl andphenylene groups in the aforedescribed base stocks can be partially ortotally replaced with a heterocyclic group such as thiophene andpyridene.

Typical examples of polyphenyl ethers, that is, when A, A A and A areoxygen and e has a value of 1 are those having all their ether linkagesin the meta position since the all-meta linked ethers are the bestsuited for many applications because of their wide liquid range and highdegree of thermal stability. However, mixtures of the polyphenyl ethers,i.e., either isomeric mixtures or mixtures of homologous ethers, canalso be used to obtain certain properties, e.g., lower solidificationpoints. Examples of the polyphenyl ethers contemplated are thebis(phenoxyphenyl) ethers, e.g.,

bis(m-phenoxyphenyl) ether;

the bis(phenoxyphenoxy)benzenes, e.g.,

m-bis(m-phenoxyphenoxy)benzene,

m-bis(p-phenoxyphenoxy)benzene,

o-bis o-phenoxyphenoxy benzene;

the bis( henoxyphenoxyphenyl) ethers,

e.g., bis[m-(m-phenoxyphenoxy)phenyl] ether,

bis pp-phenoxyphenoxy phenyl] ether,

m-[ (m-phenoxyphenoxy) (o-phenoxyphenoxy] ether and thebis(phenoxyphenoxyphenoxy)benzenes, e.g.,

m-bis [mm-phenoxyphenoxy) phenoxy] benzene,

p-bis [p- (m-phenoxyphenoxy phenoxy]-benzene,

m-bis [m- (p-phenoxyphenoxy phenoxy] benzene and1,3,4-triphenoxybenzene.

It is also contemplated that mixtures of the polyphenyl ethers can beused. For example, mixtures of polyphenyl ethers in which thenon-terminal phenylene rings (i.e., those rings enclosed in the bracketsin the above structural representation of the polyphenyl etherscontemplated) are linked through oxygen atoms in the meta and parapositions, have been found to be particularly suitable as lubricantsbecause such mixtures possess lower solidification points and thusprovide compositions having wider liquid ranges. Of the mixtures havingonly meta and para linkages, a preferred polyphenyl ether mixture ofthis invention is the mixture of S-ring polyphenyl ethers where thenon-terminal phenylene rings are linked through oxygen atoms in the metaand para position and composed, by weight, of aboutm-bis(m-phenoxyphenoxy)benzene, 30% m-[(m phenoxyphenoxy)(pphenoxyphenoxy)]benzene and 5% m-bis(p-phenoxyphenoxy)benzene. Such amixture solidifies at about -10 F. whereas the three components solidifyindividually at temperatures above normal room temperatures.

Examples of substituted polyphenyl ethers arel-(pmethylphenoxy)-4-phenoxybenzene, 2,4 diphenoxy 1 methylbenzene,bis[p-(p-methylphenoxy)phenyl] ether, bis[p-(p-tert-butylphenoxy)phenyl]ether and mixtures thereof.

Typical examples of phenoxybiphenyl compounds, that is, when 2 has avalue of 0 and A, A A and A are oxygen are 3,3'-diphenoxybiphenyl,3,2'-diphen0xybiphenyl, 3,4- diphenoxybiphenyl, 3,4-diphenoxybiphenyl,o-, mand pphenoxybiphenyl and triand tetra-substituted phenoxybiphenyls.It is also contemplated that mixtures of the above phenoxybiphenyls canbe utilized as base stocks, for example, mixtures containing from 1 to25% of a monophenoxybiphenyl, from 25% to of a diphenoxybiphenyl havingat least one phenoxy group in the meta position with respect to thebiphenyl nucleus and from 1 to 40% of a triand/ or tetra-substitutedphenoxybiphenyl.

Typical examples of polyphenylthioethers, that is, when A, A A and A aresulfur and e has a value of l are o-bis-(phenylrnercapto)benzene,m-bis(phenylmercapto)benzene, bis-(m-phenylrnercaptophenyl) sulfide,m-phenylmercaptophenyl-p-phenyl-mercaptophenyl sulfide, thetrisphenylmercaptobenzenes, such as 1,2,4-trisphenylmercaptobenzene,m-bis (p-phenylmercaptophenyl'mercapto) benzene,m-bis(m-phenylmercaptophenylmercapto)benzene, bis [m-(m-phenylmercaptophenylmercapto phenyl] sulfide,m-(m-c'hloropheny1mercapto)m-phenylmercaptobenzene, m-chlorodiphenylsulfide, bis(o-phenylmercaptophenyl) sulfide,m-bis(m-phenylmercaptophenylmercapto)benzene, 1,2, 3 -tris phenylmercapto -benzene, o-bis(o-phenylmercaptophenylmercapto)benzene,m-bis(p-phenylmercaptophenylmercapto)benzene and mixtures thereof.

Typical examples of phenylmercaptobiphenyls, that is, where e has avalue of 0 and A, A A and A are sulfur are3,3'-bis(phenylmercapto)rbiphenyl, 0-, m-, and pphenylmercapto-biphenyl, 3,4-phenylmercaptobiphenyl, 3,2diphenylmercaptobiphenyl, m-chloro-phenylmercapto3-phenylmercaptobiphenyl and mixtures thereof.

Typical examples of mixed polyphenyl ether-thioethers, that is, where ehas a value of l and at least one of the chalkogens represented by A, AA and A is dissimilar with respect to any other chalkogen are Typicalexamples of a mixed phenoxy-thiophenoxybiphenyl, that is, where e has avalue of 0 and one of the chalkogens represented by A, A A and A isdissimilar with respect to any other chalkogen arephenylmercaptophenoxybiphenyl,o-phenylmercaptophenyl-m-phenoxyphenoxybiphenyl and mixtures thereof.

It is also contemplated within the scope of this invention that theaforedescribed base stocks "can be blended together to provide mixturescomprising two or more of the above base stocks. A typical mixture of apolyphenyl thioether and a mixed polyphenyl ether-thioether is one whichcontains by weight from about 45% to about 55% n1- phenoxyphenylm-p'henylmercaptophenyl sulfide, from about to aboutbis(m-phenylmercaptophenyl) sulfide and from about 18% to about 25bis(m-phenoxyphenyl) sulfide. Particularly useful mixtures are thosecontaining the above mixtures and m-bis(phenylmercapto)benzene in aboutequal weight proportions. Typical examplesof mixtures containingpolyphenyl thioethers, a mixed polyphenyl ether-thioether andhalogenated polyphenyl ethers which are suitable as lubricants underhigh temperature conditions are as follows in weight percent:

It is also contemplated that any of the individual base stocks asdescribed above or mixtures thereof in admixture with additives of thisinvention can also be utilized to provide compositions of thisinvention.

The followng non-limiting example will illustrate a preparaton of an azocompound of this invention.

Example 1 To a 2-liter reaction flask equipped with stirrer, additionfunnel and reflux condenser was added grams of zinc dust, 120 grams of asolution consisting of 50% potassium hydroxide in water and 600 ml. ofethanol. To the flask was then added 48 grams of m-phenoxynitrobenzeneover a period of about 30 minutes. The mixture was heated to the refluxtemperature of ethanol and the reaction was continued for an additional8 hours. The reaction mixture was filtered to remove the zinc dust andthe 3,3'-diphenoxyazobenzene crystallized upon cooling of the ethanolsolution. The 3,3'-diphenoxyazobenzene was recrystallized from anacetone-ethanol mixture. The 3,3-diphenoxyazobenzene had the followinganalysis: Percent carbon, 78.1; percent hydrogen, 4.83; percentnitrogen, 7.60.

The azo compound of the example and additional azo compounds wereblended into base stocks to evaluate the oxidative stability of theresulting functional fluid compositions.

Following the procedure of Example 1, additional phenoxy and thiophenoxyazo compounds of this invention can be prepared. Thus, 3,3-dithiophenoxyazobenzene is prepared by the reduction of In-thiophenoxy nitrobenzene.Additionally, 3,3-(m-phenoxyphenoxy) azobenzene can be prepared by thereduction of 3-(m-phenoxyphenoxy) nitrobenzene.

The major bench scale method used for evaluating the oxidative stabilityof a lubricant is the procedure given in Federal Test Method, StandardNo. 791, Method No. 5308 according to which the lubricant to be testedis heated at a specified temperature in the presence of certain metalsand oxygen and the viscosity increase of the lubricant is determined.Additionally, information as to the corrosivity of a lubricant to metalsand the degree of sludge and deposit formation can also be obtained.

Various functional fluid compositions containing an azo compound weretested according to the above procedure except that the temperature washeld at 650 F. instead of 500 F. and the metal specimens used were, asspecified in said procedure, steel, copper, silver, titanium, magnesiumalloy and aluminum alloy. The viscosity of the fluid before and aftertesting was determined at F.

In Table I the percent stabilization is determined by the followingformula:

Percent stabilization:

7 percent viscosity increase of the base stock plus azo compound after24 hours at 65 F.

In Table I the base stock that was used was a mixture of -ringpolyphenyl ether.

fective in controlling oxidative degradation of the base stock as isevidenced by the degree of stabilization of the compositions of thisinvention. Stabilization of a base stock is of particular importance inthe many uses of Viscosity increase determined at 18 hours.

2 Minus sign signifies additive is prooxidant.

Viseosity increase determined at 21 hours.

A hearing test was run which was modified from MIL-- 11-27502. The testtime was 100 hours using an ERDCO bearing. The test conditions forExample 8 were a bearing temperature of 600 F., a bulk oil temperatureof 600 F. and an oil in temperature of 550 F. The test conditions forExample 9 are the same as for Example 8 except that the bearingtemperature was increased to 650 F. In Table II the base stock that wasused was a mixture of S-ring polyphenyl ether. The stabilizer that wasused was 3,3- diphenoxyazobenzene.

1 Test terminated and viscosity determined at 62.5 hours.

2 Viscosity determined at 100 hours.

As is demonstrated by Tables I and II, it is clearly evident that theincorporation of an azo compound of this invention into a base stockprovides a functional fluid composition which has a high degree ofresistance towards oxidative degradation and, therefore, a greatlyextended useful life. In regard to the extension of useful life, it hasbeen found that the test procedure described above correlates quite wellwith the results obtained under full-scale aircraft gas turbine bearingtests and under conditions of actual use. It has been found that themagnitude of change in viscosity at 100 F. as measured by the testprocedure is representative of the extent of increased service lifeobtainable under actual conditions. Thus, for example, the decrease inviscosity increase of a composition incorporating an azo compound ofthis invention was on the order of about three times less than the basestock viscosity increase for the same period of time. Of equalsignificance are the results as are set out with respect tophenolic-type antioxidants, which antioxidants have been effective inthe prior art for inhibiting oxidative degradation of organicsubstances. The results in Table I with respect to these phenolicantioxidants show that the rate of oxidation of a composition whichincorporates these antioxidants is higher than the neat base stockalone. The higher rate of oxidation with the phenolic antioxidantsdemonstrates that a compound can act as a prooxidant in systemsoperating at high temperatures. Of equal significance are the resultsset out in Table II since the hearing test correlates quite well withactual gas turbine performance in measuring the overall deposit ratingand viscosity changes which would be expected to occur in actual use.Thus, the test of the neat base stock had to be terminated at the end of62.5 hours with a substantial increase in viscosity. The compositions ofthe invention maintained the required temperature-viscosity relationshipand did not become too thick on prolonged use thereby maintaining properlubrication of mechanical parts in contact with the fluid.

Tables I and II in addition significantly demonstrate that the azocompounds at low concentrations are effunctional fluids since therequired fluid characteristics can be maintained over extended periodsof time during use by the incorporation of an azo compound. Theincorporation of an azo compound into a base stock to control oxidativedegradation is of particular importance since when fluid degradationoccurs, such degradation can manifest itself in numerous ways amongwhich are viscosity change, increase in acid number, formation ofinsoluble materials, increased reactivity and discoloration. In a fluidsystem the particular properties of a fluid have to be maintained inorder to continue useful operation in the particular system in which thefluids are employed. Thus, changes in viscosity can be produced by fluiddegradation whereby polymeric products with high molecular weights areproduced in the fluid system. Such high molecular weight products oftenbecome inprecipitation or sludging of the insoluble material. Suchprecipitation and sludging plugs filters and causes deposits to form onmoving parts which are lubricated by the fluid thereby causinginadequate lubricating and interference with the proper functioning ofthe parts. Increased chemical reactivity is observed on fluiddegradation as well as a build-up in acid number of the fluid. Suchincreased chemical reactivity and high acid number allows the particularsystem which incorporates the fluid to be chemically attacked by thefluid thereby causing pitting, wear and alterations of the closetolerances of mechanical members in contact with said fluid. Thus,premature overhaul of mechanical parts can be a direct consequence offluid degradation. It is, therefore, of particular importance that abase stock be stabilized so as to extend the useful life of a fluid in afunctional fluid system.

As a result of the excellent stabilization of functional fluids whichincorporate an azo compound, lubrication of gas turbine engines isobtained over extended periods of time. Thus, this invention relates toa novel method of lubricating gas turbine engines which comprisesmaintaining on the bearings and other points of wear a lubricatingamount of a composition of this invention.

In addition, as a result of the excellent control of oxidativedegradation utilizing the functional fluid compositions of thisinvention, improved hydraulic pressure devices can be prepared inaccordance with this invention which comprise in combination a fluidchamber and an actuating fluid composition in said chamber, said fluidcomprising a mixture of one or more of the base stocks hereinbeforedescribed and a minor amount, suflicient to stabilize said base stock,of an azo compound. In such a system, the parts which are so lubricatedinclude the frictional surfaces of the source of power, namely the pump,valves, operating pistons and cylinders, fluid motors, and in somecases, for machine tools, the ways, tables and slides. The hydraulicsystem may be of either the constant-volume of the variable-volume typeof system.

The pumps may be of various types, including centrifugal pumps, jetpumps, turbine vane, liquid piston gas compressors, piston-type pump,more particularly the variable-stroke piston pump, thevariable-discharge or variable displacement piston pump, radial-pistonpump, axial-piston pump, in which a pivoted cylinder block is adjustedat various angles with the piston assembly, for example, the VickersAxial-Piston Pump, or in which the mechanism which drives the pistons isset at an angle adjustable with the cylinder block; gear-type pump,which may be spur, helical or herringbone gears, variations of internalgears, or a screw pump; or vane pumps. The valves may be stop valves,reversing valves, pilot valves, throttling valves, sequence valves,relief valves, Servo valves, non-return valves, poppet valves orunloading valves. Fluid motors are usually constantor variable-dischargepiston pumps caused to rotate by the pressure of the hydraulic fluid ofthe system with the power supplied by the pump power source. Such ahydraulic motor may be used in connection with a variable-discharge pumpto form a variable-speed transmission. It is, therefore, especiallyimportant that the frictional parts of the fluid system which arelubricated by the functional fluid be protected from damage. Thus,damage brings about seizure of frictional parts, excessive wear andpremature replacement of parts.

The fluid compositions of this invention when utilized as a functionalfluid can also contain dyes, pour point depressants, metal deactivator,acid scavengers, antioxidants, defoamers in concentration suflicient toimpart antifoam properties, such as from about to about 100 parts permillion, viscosity index improvers such as polyalkylacrylates,polyalkylmethacrylates, polycyclic polymers, polyurethanes, polyalkyleneoxides, substituted and unsubstituted polyphenylene oxides andpolyesters, lubricity agents and the like.

It is also contemplated within the scope of this invention that the basestocks as aforedescribed can be utilized singly or as a fluidcomposition containing two or more base stocks in varying proportions.The base stocks can also contain other fluids which include, in additionto the functional fluids described above, fluids derived from coalproducts, and synthetic oils, e.g., alkylene polymers (such as polymersof propylene, butylene, etc., and the mixtures thereof), alkyleneoxide-type polymers (e.g., propylene oxide polymers) and derivatives,including alkylene oxide polymers prepared by polymerizing the alkyleneoxide in the presence of water or alcohols, e.g., ethyl alcohol, alkylbenzenes (e.g., monoalkyl benzene such as dodecyl benzene, tetradecylbenzene, etc.), and dialkyl benzenes (e.g., n-nonylZ-ethylhexylbenzene); polyphenyls (e.g., biphenyls and terphenyls),halogenated benzene, halogenated lower alkyl benzene, halogenatedbiphenyl and monohalogenated diphenyl ethers.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

The embodiments of this invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A composition comprising (A) a major amount of a base stock selectedfrom the group consisting of (1) polyphenyl ethers, (2) phenoxybiphenylsand (3) mixtures thereof; and

(B) an oxidation inhibiting amounts of an azo compound selected from thegroup consisting of (1) a compound represented by the structure whereina and b are whole numbers having a value of 0 to 5 and R and R are eachselected from substituents selected from the group consisting of alkyl,aryl, amino, N-phenylamino, N- dimethylamino, cyano, nitro, halogen,sulfonic, carboxyl, carboalkoxy, phenoxy, phenylmercapto, alkoxy,hydroxyl, trifluoromethyl, alphacumyl and mixtures thereof and (2) azonaphthalene.

2. A composition of claim 1 wherein each R contains from 0 to 18 carbonatoms and a and b each have a value of from 0 to 2.

3. A composition of claim 2 wherein R and R each have from 0 to 9 carbonatoms.

4. A composition of claim 3 wherein R and R are each selected from thegroup consisting of alkyl, phenyl, phenoxy, phenylmercapto, bromo,hydroxyl, alpha-cumyl and trifluoromethyl.

5. A composition of claim 4 wherein a and b each have a value of from 0to 1.

6. A composition of claim 5 wherein the azo compound is azobenzene.

7. A composition of claim 4 wherein the azo compound is (B) (1) and Rand R are each selected from the group consisting of phenoxy,phenylmercapto and bromo.

8. A composition of claim 7 wherein R and R are selected from phenoxyand phenylmercapto and occupy the 2- and 2-position relative to theazobenzene nucleus.

9. A composition of claim 1 wherein the base stock is (A) (1).

10. A composition of claim 9 wherein (A)(1) is an unsubstitutedpolyphenyl ether containing from 3 to 7 aromatic rings.

11. A composition of claim 4 wherein the base stock is (A) (1) and (A)(1) is an unsubstituted polyphenyl ether containing from 3 to 7 aromaticrings.

12. A composition of claim 7 wherein the base stock is (A) (1) and (A)(1) is an unsubstituted polyphenyl ether containing from 3 to 7 aromaticrings.

13. A composition of claim 11 wherein the polyphenyl ether ism-bis(m-phenoxyphenoxy)benzene.

14. A method of lubricating a gas turbine engine which comprisesmaintaining on points of wear a lubricating amount of a composition ofclaim 1.

15. A method of lubricating a gas turbine engine which comprisesmaintaining on points of wear a lubricating amount of a composition ofclaim 9.

16. A method of lubricating a gas turbine engine which comprisesmaintaining on points of Wear a lubricating amount of a composition ofclaim 11.

References Cited UNITED STATES PATENTS 2,718,501 9/1955 Harle 252473,198,734 8/1965 Morway 25252X OTHER REFERENCES Kor ger et al.,Oxidation of Naphthenes, Chemical Abstracts, vol. 44 (1950), pp. 1683,1684 and 1685.

DANIEL E. WYMAN, Primary Examiner.

W. H. CANNON, Assistant Examiner.

